RESPONSE OF MEAN AND PHASIC CORONARY ARTERIAL BLOOD FLOW TO GRADED HYPERCAPNIA IN DOGS

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Abstract
An electromagnetic flow meter was used to assess the changes in coronary blood flow in response to 4 levels of increased PaCO2 [CO2 partial pressure] in 6 dogs. Mean, diastolic and systolic flow all increased during hypercapnia; the increase was maximal at mean PaCO2 11.3 kPa. Mean and diastolic coronary vascular resistances decreased progressively as PaCO2 increased; systolic resistance decreased with lower levels of hypercapnia and returned to control at the greatest PaCO2. The O2 available to the myocardium was increased markedly during hypercapnia and coronary sinus PO2 [O2 partial pressure] increased reflecting a reduction in myocardial O2 extraction. Myocardial O2 consumption was unchanged. Cardiac output was increased significantly only at the greatest PaCO2. Total body O2 handling was not altered significantly.